1. Field of the Invention
The present invention relates to a magnification observation apparatus such as a digital microscope and a microscope that images and displays a magnified image and a method for creating a high tone image file.
2. Description of the Relating Art
A magnification observation apparatus that magnifies and displays a subject such as a sample including a minuscule object and a workpiece utilizes an optical microscope and digital microscope using an optical lens, and the like. The digital microscope receives reflected light or transmitted light from an observation target fixed at an observation target fixing unit entering through an optical system with a light receiving device such as a CCD, which electrically reads the light for every pixel arranged two-dimensionally, and displays the electrically read image on a display unit such as a display (e.g., see Japanese Laid-Open Patent Publication No. 2002-135648).
The sensitivity region of the light receiving device such as a CCD is limited to a particular range, whereas the sensitivity range of a human eye is wider. Thus, the range that can be represented (dynamic range) of the image imaged with the CCD is limited compared to the human eye. For instance, the dynamic range is eight bits in a general JPEG image. In this case, if the tone of the image to be imaged exceeds such a range, saturation occurs, thereby causing underexposure, overexposure, halation, and the like. In order to solve such problems, used is a high dynamic range image (hereinafter referred to as “HDR image”) in which a plurality of low tone images are imaged with the dynamic range of the luminance region changed is synthesized to obtain a high tone image. The HDR image is obtained by synthesizing a plurality of images at different levels of exposure of the same subject and integrating the darkest shadow (black) to an extremely bright highlight (white) into one HDR image in a wide dynamic range. For instance, a plurality of eight bit images is synthesized to generate a high tone HDR image of sixteen bits or thirty-two bits, and such an image is saved. For example, overexposure occurs at the metal portion in the image shown in FIG. 1, and underexposure occurs in the image shown in FIG. 2. When such images are synthesized, the HDR image as shown in FIG. 3 can be generated. The portions of overexposure and underexposure in the original image are clearly represented in the HDR image of FIG. 3.
When displaying the HDR image synthesized in the above manner on a monitor and the like, tone conversion (tone mapping) needs to be performed to a color range that can be displayed on the monitor, that is, a low dynamic range. Since only 16.77 million colors can be represented in twenty-four bit color, and only 256 colors in the case of eight bits in a general personal computer, the HDR image of thirty-two bits is handled as twenty-four bits or eight bits through tone mapping.
The file format for saving high tone image data such as the HDR image includes thirty-two bits floating point TIFF, log Yuv which obtains Yuv data by taking the logarithm of a synthesized image and converting it to a whole number, and Open EXR using the sixteen bits floating point, each of which is a uncompressed or lossless compression format.
[Patent document 1] Japanese Laid-Open Patent Publication No. 2002-135648
[Patent document 2] Japanese Laid-Open Patent Publication No. 2002-223387
However, since such image file formats are not versatile, such formats cannot be displayed in most commercially available general purpose image display programs. Furthermore, the data size is large since the lossy compression technique such as JPEG is not used. In this regard, a technique of introducing JPEG, JPEG 2000, or the like to perform data compression has been proposed, but it is still difficult to use since the file format is not a general file format such as TIFF and Open EXR. Moreover, when tone-converting a high tone image to a low tone image and displaying the same on a monitor and the like, image processing, such as enhancement of fine patterns (textures) in the high tone image, is sometimes performed. In this case, the texture enhancement process needs to be performed after extracting texture components of the high tone image from the HDR image. Specifically, the texture extracting process is performed after once reading the file from the hard disc drive of a computer. A significant amount of time is required from opening the file to actually displaying the file on the monitor, as a great amount of calculation is required for such an extraction task. Not limited to the texture enhancement process, a great number of drawing parameters need to be set when drawing a high tone image. Such drawing parameters can be automatically or manually set in tone conversion, but conventionally, the user needs to manage the records by, e.g., taking notes on what drawing parameter is set for which high tone image, which is a very cumbersome task.